1. Field of the Invention
The present invention relates to an electrophotographic apparatus which can be used in printers, facsimile equipment or similar equipment.
2. Discussion of Related Art
A two-component development method using a developer formed of a toner and a carrier has so far been widely used in electrophotography, but in recent years development of a mono-component development method has been in progress in order to make image forming units smaller and less costly.
FIG. 28 shows the electrophotographic apparatus which uses such a mono-component development method, which was disclosed by the inventors of the present invention in the Japanese Patent Application "Heisei 3-345990." In FIG. 28, an electrostatic latent image holding member of an organic photoconductor drum 1 has phthalocyanine dispersed in a binder resin of polyester group. A magnet 2 has the axis thereof fixed coaxially with the organic photoconductor drum 1. A corona charger 3 charges the organic photoconductor drum 1. A grid electrode 4 controls charge potential of the organic photoconductor drum 1. The electrophotographic apparatus also includes a signal light 5 (also referred to herein as "laser light"), and a developer reservoir 6. A magnetic one-component toner 7 (also referred to in this application as a "one component magnetic toner" or as "toner") serves as a developer. A damper 8 makes smooth the flow of the toner 7 inside the developer reservoir 6, and also prevents the toner 7 from being packed due to its own weight and filling between the organic photoconductor drum 1 and a removing roller 9.
The magnet 2 forms a magnetic pole in an area of .theta.=10.degree. opposite to the developer reservoir 6. The removing roller 9 is made of aluminum and has a magnet 10 therein. An AC high voltage power source 11 applies a voltage to the removing roller 9. A scraper 12 made of polyester film scrapes the toner from the removing roller 9. A transfer corona charger 13 transfers toner images formed on the organic photoconductor drum 1 to paper.
With the help of FIG. 28, an explanation will be made hereunder of how the electrophotographic apparatus described above operates. The organic photoconductor drum 1 is charged to -500 V by means of the corona charger 3 and the grid electrode 4. An electrostatic latent image is formed by irradiating the laser light 5 on the organic photoconductor drum 1. The toner 7 is deposited on the surface of the organic photoconductor drum 1 by magnetic force in the developer reservoir 6. Next, the organic photoconductor drum 1 is caused to pass the front of the removing roller 9. At this time, an AC voltage of 750.sub.O-p (1 kHz in frequency) with a DC voltage of -350 V superimposed thereon is applied to the removing roller 9 from the AC high voltage power source 11. Then, the toner 7 is removed from the organic photoconductor drum 1 to the removing roller 9, and toner images with a positive-negative picture reversal are left only on the image areas of the organic photoconductor drum 1. The toner 7 deposited on the removing roller 9, which is rotating in the direction of the arrow, is scraped off by the scraper 12, and returned to the developer reservoir 6 for use in the image forming steps to follow. The toner images thus formed on the organic photoconductor drum 1 are transferred to paper (not shown in FIG. 28) by the transfer corona charger 13, and then thermally fixed by means of a fixing equipment (not shown in FIG. 28).
However, when printing is performed by the electrophotographic apparatus, the image density of solid-image is low under a high temperature and high humidity environment (33.degree. C., 85% relative humidity (RH), for example), and background development is found to increase gradually on the printed images.
None of the prior art electrophotographic apparatus produces high quality images having high image density, which are substantially free of non-uniformity in density. Similarly, most of the prior art electrophotographic apparatus exhibits unevenness in the force transporting the toner particles on the electrostatic image holding member.